The present invention generally relates to a marking utensil. In particular, the present invention relates to a marking utensil that provides hydrostatic stability in response to changes in temperature and pressure.
It is well known to provide a pen having free ink that a user may selectively apply to a substrate such as paper. Such known pens typically include a reservoir for storing the ink and a channel for ducting the ink from the reservoir to a marking tip. The ink of such known pens typically has a vapor pressure such that the ink, and any air in the reservoir, expands and contracts in response to changes in ambient temperature and pressure. Such expansion and contraction of air may cause the ink to leak from the writing tip of the pen.
Other such known pens include a buffer for storing excess ink in response to changes in ambient temperature and pressure. The excess ink is typically stored in the front of the buffer near the tip of the pen (i.e., due to gravity). However, such known pens have several disadvantages: the ink capacity of the buffer is limited such that when the buffer is full the excess ink from the pen, and the ink is often permanently stored in the buffer resulting in decreased buffer capacity and wasted ink. Another of such known pens provides for the cleaning of ink from the buffer when the pressure inside the pen is increased by venting air into the pen through an external vent. Such known pens, however, only clean a small portion of the buffer.
Accordingly, it would be advantageous to provide a hydrostatically stable pen that responds to repeated temperature and pressure changes by reducing the accumulation of ink in the buffer without substantially leaking or dripping. It would also be advantageous to provide a pen that optimizes the efficiency of the buffer by purging the buffer during changes in ambient temperature or pressure. It would also be advantageous to provide hydrostatic stability when the pen is oriented in any direction. Other advantages of the subject matter recited in the appended claims will become apparent to those skilled in the art upon review of the specification and the claims.
The present invention relates to a free ink marking instrument for dispensing a fluid including a housing having an interior defined by a wall and a reservoir for storing the fluid disposed in the housing. The instrument includes a feeder for conveying fluid to a marking tip from the reservoir. The instrument also includes a passage of reduced capillarity relative to the feeder surrounding the feeder for conveying at least one of fluid and air to the reservoir during an increasing pressure differential between air in the reservoir and the atmosphere. The instrument also includes a porous buffer disposed between the wall of the housing and the passage and configured for storing ink during periods of a decreasing pressure differential between air in the reservoir and the atmosphere. The instrument also includes a divider tube separating the buffer and the passage along a majority of the length of the buffer. The fluid and air may enter the feeder through a minor surrounding portion of the buffer during the period of the increasing pressure differential.
The present invention also relates to an ink and air conveyor for use in a free ink marking instrument for dispensing ink onto a substrate such as paper. The instrument includes a housing having an interior including a reservoir for storing the ink and a marking tip coupled to the housing. The conveyor includes a divider tube supported along an axis of the marking instrument. The conveyor also includes a feeder disposed within the divider tube and extending outwardly therefrom toward the marking tip. The conveyor also includes a buffer surrounding a portion of the feeder and extending outwardly from the divider tube. The conveyor also includes a channel adapted for conveying at least one of fluid and air located between an exterior surface of the feeder and an interior surface of the divider tube.
The present invention also relates to a method for compensating for changes in temperature and pressure in a free ink marking instrument. The instrument includes a housing having an interior defined by a wall, a reservoir for storing ink and air disposed in the housing, and a marking tip coupled to the housing. The instrument also includes a buffer having a first portion and a second portion disposed within the housing and a divider tube generally parallel to the wall of the housing. The instrument also includes a feeder configured for conveying air and ink. A first portion of the feeder extends into the divider tube and is spaced from an inner wall thereof. A second portion of the feeder is attached to an inner wall of the divider tube, and a third portion of the feeder extends outwardly from the divider tube toward the marking tip. The method includes drawing air from the atmosphere through a vent near the marking tip to the interior of the housing during periods of increasing ambient pressure or decreasing ambient temperature. The method also includes urging the air through the buffer. The method also includes urging the air from the buffer to the third portion of the feeder. The method also includes urging the air from the third portion of the feeder to the channel. The method also includes urging the air from the feeder to a space between the feeder and the inner wall of the divider tube.